A mysterious locked safe has been found by a couple buried beneath their back garden.

Heavy and rusting, the enormous safe, which is the same type as those used on the Titanic, was hidden beneath a garden pond for decades.

It was only when David Maguire, 34, spent an afternoon tirelessly shifting mounds of soil that the object finally revealed itself.

David’s wife Nikki said they can hear something is still inside from their efforts to move it across the garden and are now desperate to get in without damaging its impressive cast iron walls.

“We’d seen this bit of bronze metal poking out from where the old pond used to be for a while but just thought it was part of an old pump,” said Nikki.

“We were completely amazed when it turned out to be the top of a safe.

“My house was built in the 1920s, but this looks a lot older than that. Before my house was built there was flats here. I don’t know if it’s been brought up here to be buried especially when they were building the houses. We’ve just got no idea,” added Nikki, who lives at Hadrian Place in Sheriff Hill, Gateshead.

The safe is almost a metre tall and is made by Milners, an historic company that began in 1814 by Thomas Milner and became famous for developing the world’s first fire proof safes.

He would wow crowds with stunts involving elaborate street bonfires to demonstrate that his safes could protect anything that was inside.

Five of them were used onboard the Titanic ship which sank in 1912.

On the front of the one found in the Maguires garden is a plaque which reads ‘Milners of London, Manchester and Liverpool’ and ‘Patent fire resisting special safe’.

However, with no key found alongside it, its contents remain a secret.

Nikki, 32, who works for St Oswald’s Hospice, said: “We’ve lived here for four years and at the bottom of the garden was a pond. We’ve got a little girl Alice, who is three, so we drained it and just left the area, which became a bit of a mess to be honest.

“Then David said he was going to dig out the metal and it wasn’t until he had removed all the soil from around it that we could finally see what it was.

“It’s so heavy to lift, we can barely do it between us, so we’ve had to roll it across the garden and we can hear there’s something inside. It could just be soil after all these years, but it might be something interesting, you never know!”

Despite its rusty appearance, the safe could date from anywhere between the mid 19th century and 1955, when the Milner company merged with the firm Chatwood, although older designs had a distinctive arch on the front door.

Those in a good condition currently sell for hundreds of pounds on online auction site eBay.